Z. H. Zhu

Dielectric loaded graphene plasmon waveguide

Dielectric loaded graphene plasmon waveguide (DLGPW) is proposed and investigated. An analytical model based on effective-index method is presented and verified by the finite element method simulations. The mode effective index, propagation loss, cutoff wavelength of higher order modes and single-mode operation region were derived at mid-infrared spectral region. By changing Fermi energy level, the propagation properties of fundamental mode could be tuned flexibly. The structure of the DLGPW is simple and easy for fabrication. It provided a new freedom to manipulate the graphene surface plasmons, which may led to new applications in actively tunable integrated optical devices.

Electrically controlling the polarizing direction of a graphene polarizer

We theoretically demonstrate a polarizer with an electrically controllable polarizing direction in the far infrared range using two orthogonal periodic arrays of graphene ribbons, which have different widths and are supported on a dielectric film placed on a thick piece of metal. The operation mechanism originates from the polarization-dependent resonant absorption of the two orthogonal graphene ribbons, which can be respectively controlled with different external bias voltages. The operation wavelength can be expanded to terahertz (THz) radiation.

Monolayer-graphene-based perfect absorption structures in the near infrared.

Subwavelength perfect optical absorption structures based on monolayer-graphene are analyzed and demonstrated experimentally. The perfect absorption mechanism is a result of critical coupling relating to a guided mode resonance of a low index two-dimensional periodic structure. Peak absorption over 99% at wavelength of 1526.5 nm with full-width at half maximum (FWHM) about 18 nm is demonstrated from a fabricated structure with period of 1230 nm, and the measured results agree well with the simulation results. In addition, the influence of geometrical parameters of the structure and the angular response for oblique incidence are analyzed in detail in the simulation. The demonstrated absorption structure in the presented work has great potential in the design of advanced photo-detectors and modulators.

Thermal transport properties of suspended graphene

Electrically biased graphene has been studied experimentally as a novel emitter of thermal radiation. However, there is as yet no systematic theory that quantifies the thermal radiation, heat transfer, and electrical properties of electrically biased graphene. To study the thermal transport properties systematically, a heat conduction model is developed and exploited in this paper. The temperature distribution and heat conduction coefficient of graphene under different bias voltages are obtained using our theoretical model. The I–V curve and the relationship between the radiant power and input voltage of graphene are then obtained. This work could help design a novel efficient wavelength-adjustable thermal radiation source.Electrically biased graphene has been studied experimentally as a novel emitter of thermal radiation. However, there is as yet no systematic theory that quantifies the thermal radiation, heat transfer, and electrical properties of electrically biased graphene. To study the thermal transport properties systematically, a heat conduction model is developed and exploited in this paper. The temperature distribution and heat conduction coefficient of graphene under different bias voltages are obtained using our theoretical model. The I–V curve and the relationship between the radiant power and input voltage of graphene are then obtained. This work could help design a novel efficient wavelength-adjustable thermal radiation source.

Electrically tunable graphene polarization beam splitting utilizing Brewster effect

We theoretically and numerically demonstrate that electrically tunable polarization beam splitting (PBS) can be realized by the structure of graphene ribbons supported on a dielectric film. The mechanism comes from the fact that the TE mode (like S wave polarization) is highly reflected by the plasmonic resonances of graphene ribbons, and the TM mode (like P wave polarization) is largely transmitted utilizing the Brewster effect. The results of full-wave numerical simulations reveal that a transmission splitting ratio of about 20 dB and a reflection splitting ratio of around 28 dB can be achieved with the Brewster angle incident. The proposed polarization beam splitting can be electrically tuned, which facilitates many practical applications.